1. Field of the Invention
The present invention relates to a film formation apparatus and method for a semiconductor process for forming a thin film on a target substrate, such as a semiconductor wafer. The term “semiconductor process” used herein includes various kinds of processes which are performed to manufacture a semiconductor device or a structure having wiring layers, electrodes, and the like to be connected to a semiconductor device, on a target substrate, such as a semiconductor wafer or a glass substrate used for an LCD (Liquid Crystal Display) or FPD (Flat Panel Display), by forming semiconductor layers, insulating layers, and conductive layers in predetermined patterns on the target substrate.
2. Description of the Related Art
In manufacturing semiconductor devices for constituting semiconductor integrated circuits, a target substrate, such as a semiconductor wafer, is subjected to various processes, such as film formation, oxidation, diffusion, reformation, annealing, and etching. Jpn. Pat. Appln. KOKAI Publication No. 2004-6801 discloses a semiconductor processing method of this kind performed in a vertical heat-processing apparatus (of the so-called batch type). According to this method, semiconductor wafers are first transferred from a wafer cassette onto a vertical wafer boat and supported thereon at intervals in the vertical direction. The wafer cassette can store, e.g., 25 wafers, while the wafer boat can support 30 to 150 wafers. Then, the wafer boat is loaded into a process container from below, and the process container is airtightly closed. Then, a predetermined heat-process is performed, while the process conditions, such as process gas flow rate, process pressure, and process temperature, are controlled.
In recent years, owing to the demands of increased miniaturization and integration of semiconductor integrated circuits, it is required to alleviate the thermal history of semiconductor devices in manufacturing steps, thereby improving the characteristics of the devices. For vertical processing apparatuses, it is also required to improve semiconductor processing methods in accordance with the demands described above. For example, there is a CVD (Chemical Vapor Deposition) method for a film formation process, which performs film formation while intermittently supplying a source gas and so forth to repeatedly form layers each having an atomic or molecular level thickness, one by one, or several by several (for example, Jpn. Pat. Appln. KOKAI Publication Nos. 6-45256 and 11-87341). In general, this film formation method is called ALD (Atomic layer Deposition), which allows a predetermined process to be performed without exposing wafers to a very high temperature.
FIG. 13 is a timing chart of the gas supply and RF application of a conventional film formation method, where dichlorosilane (DCS) and NH3 are supplied as a silane family gas and a nitriding gas, respectively, to form a silicon nitride film (SiN). As shown in FIG. 13, DCS and NH3 gas are alternately and intermittently supplied into a process container with purge periods interposed therebetween. When NH3 gas is supplied, an RF (radio frequency) is applied to generate plasma within the process container so as to promote a nitridation reaction. Specifically, when DCS is supplied into the process container, a layer with a thickness of one molecule or more of DCS is adsorbed onto the surface of wafers. The superfluous DCS is removed during the purge period. Then, NH3 is supplied and plasma is generated, thereby performing low temperature nitridation to form a silicon nitride film. These sequential steps are repeated to complete a film having a predetermined thickness.
According to the film formation method described above, it is possible to obtain relatively good step coverage, and also improve the film quality, because the number of Si—H bonds in the film is reduced due to a lower temperature, as compared to a case where a CVD film formation method is performed at a higher temperature. However, conventional film formation methods of this kind can attain only a very low film formation rate and thus low throughput, in spite of plasma being used to promote the reaction.